A gasifier which gasifies carbonaceous solid fuel such as coal under a pressurized environment needs to be disposed in a pressure vessel. Such a gasifier is provided with a heat exchanger installed downstream of the gasifier in order to lower the temperature of gas which is generated in the gasifier to a heatproof temperature of a general steel pipe.
The heat exchanger is formed by a heat exchanger tube which is referred to as a Syn Gas Cooler (SGC), is an assembly (a heat exchanger tube group) of a furnace wall (a SGC peripheral wall) and the heat exchanger tubes (SGCs) installed inside, and is configured such that in a furnace wall inside downstream part of the gasifier, a fluid such as water flowing inside the heat exchanger tube absorbs heat from high-temperature raw syngas flowing inside of the furnace wall, thereby lowering a gas temperature.
The heat exchanger tube group of the heat exchanger has an element structure, and one element assembly is referred to as a bank. Further, the banks are classified to have several kinds of specification according to a temperature zone of a fluid (water, steam, or the like) flowing through the heat exchanger tube. The heat exchanger tube group configuring an element is assembled into a bank by being connected to a steel pipe which is referred to as a header, in a space which is referred to as an annulus portion which is formed between the outer peripheral surface of the furnace wall and the inner peripheral surface of a pressure vessel.
Further, respective banks having different specifications are connected to the outside of the gasifier by connecting the respective headers by a steel pipe which is referred to as a connecting pipe and finally making the steel pipe go through the pressure vessel.
Further, the heat exchanger which is installed in the gasifier generally has a structure in which a bank is disposed in a furnace wall having, for example, a rectangular cross-section. However, for example, as disclosed in the following PTL 1, there is also a structure in which a bank is disposed in a hexagonal flue.